Sigma 1 and sigma 2 binding sites are expressed in high density in a wide variety of human and rodent tumor cell lines. Technetium-99m (Tc-99m) radiopharmaceuticals are utilized widely in the clinical diagnosis and prognosis of disease. In vivo detection of cancerous cells containing sigma receptors may be possible if high affinity, selective Tc-99m complexes can be identified. Outside the scope of this developmental project, but part of our long-range goals is the translation of the diagnostic Tc-99m complexes into radiotherapeutic analogs utilizing Rhenium-188 (Re-188). Re-188 possesses a suitable half-life and strong beta-emissions capable of delivering a high dose to tissues. It also has an associated 1,photon (155 KeV, 15%), making it possible to follow biodistribution with the same scintigraphic equipment as used for Tc-99m. Therapeutic measures could be initiated upon substitution of Tc with Re-188 in high affinity sigma receptor binding complexes. Our specific aims for this developmental project are: 1) to synthesize and characterize Tc-99m and Tc-99 labeled chelates derived from analogs of sigma receptor binding ligands; 2) to determine the biodistribution of the Tc-99m complexes in mouse and the in vitro affinity of the Tc-99 complexes for the sigma 1 and sigma 2 receptors; 3) to correlate the structure of the complexes with the biological results.